132 Mr. G. C. Griffiths on the Frenulum of the Lepidoptera. 
great, for the wings which before presented one broad 
strong surface to the breeze, would after the amputation 
of the spina lose much power by the escape of the air 
between them, and would probably be bent or displaced 
if the wind were at all boisterous. 
Another point having a bearing upon the question of 
the use of this apparatus was noticed in a female specimen 
of Deilephila ewphorbix, and might no doubt be observed 
in many other species. The insect resting on a flat surface 
with its wings outspread held the anterior margin of the 
hindwings in such a position as to be just in contact with 
the costal nervure of the forewings, but on being dis- 
turbed it prepared for flight by bringing forward the 
front pair slightly, and strongly depressing their points. 
This clearly forces the spinulz into close contact with 
the fasciculus of long scales destined to receive and hold 
them, and thus locks the wings firmly together. This 
proceeding was gone through by the insect again and 
again on being disturbed, and is evidently its first prepara- 
tion for flight. 
In the examination of living specimens the writer was 
at first somewhat doubtful whether the male insect, if by 
accident it should withdraw its spina entirely from the 
retinaculum, would be able to replace it at will, but this 
point was cleared up by the chance discovery of a male 
specimen of Hnnomos angularia lying upon its back in a 
pool of water. On examination the spina of the left wing 
was found to be withdrawn from its retinaculum. It was 
placed in a position in which it could dry its wings and 
from time to time examined to ascertain whether the 
spina had been replaced. Before the next morning the 
moth had once more inserted it in the retinaculum. 
It seems clear from the foregoing experiments that the 
purpose of the frenulum is to hold the wings together 
during flight, and this conclusion is accepted by most 
recent writers. The organ is therefore analogous in its 
purpose to the less perfect jugum of the Trichoptera and 
Micropteryx, to the wing-hooks of the Hymenoptera and 
to the locking apparatus of Belostoma. 
Pear ave 
[The explanation faces the PLATE] 
